(a) Field of the Invention
The present invention relates to a preheating control device controlling an operation of a lamp driving device during preheating of a lamp, a lamp driving device including the same, and a preheating control method thereof.
(b) Description of the Related Art
A control method for controlling preheating of a lamp is divided into two methods. One is a linear method of linearly increasing a preheating frequency during a preheating period, and the other is a step method of increasing the preheating frequency step by step during the preheating period. Here, the preheating frequency means a frequency of a waveform for the voltage (hereinafter, lamp voltage) between both terminals of the lamp during the preheating period.
Generally, the preheating control method according to the step method may decrease the preheating time compared with the linear method. This is because the step method supplies a higher current to the filament of the lamp during the preheating period compared with the linear method.
In a case of firstly operating the lamp and a case in which the lamp is maintained in an off state for a predetermined period and is then turned on (hereinafter, a cold start), the two methods do not have the above-described problem. However, the two methods cause the above-described problem in a case (hereinafter, a hot start) in which the lamp is turned off and then is turned on after a short time. This is because the lamp voltage that is capable of turning on the lamp is different according to the temperature of the filament. In detail, as the filament temperature is increased, the lamp voltage that is capable of turning on the lamp is decreased.
Also, an operation of the lamp, that is, a period from the time that a switch (hereinafter, a lamp driving switch) controlling the turn-on to the time that the lamp is actually turned on, must be more than a predetermined threshold period that is determined by law. In the case of the cold start, a period of more than the threshold period must elapse, and then the lamp may be turned on. Accordingly, when the lamp driving switch is turned on in the general cold start, the problem that the lamp is turned on within the threshold period is not generated.
However, in the case of the hot start, the temperature of the lamp is high enough such that the lamp may be turned on at a low lamp voltage. According to the two methods, although the lamp may be turned on before the end of the threshold period, the turn-on of the lamp is suppressed by force after the threshold period in the case of the hot start.
According to the delay of the turn-on of the lamp by force, the filament of the lamp is over-preheated and unnecessary power consumption is generated by the current flowing in the filament.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.